Monoethylene glycol is used as a raw material in the manufacture of polyester fibres, polyethylene terephthalate (PET) plastics and resins. It is also incorporated into automobile antifreeze liquids.
Monoethylene glycol is typically prepared from ethylene oxide, which is in turn prepared from ethylene. Ethylene and oxygen are passed over a silver oxide catalyst, producing a product stream comprising ethylene oxide, carbon dioxide, ethylene, oxygen and water. The product stream is supplied to an ethylene oxide absorber and the ethylene oxide is absorbed by a recirculating solvent stream.
The solvent stream leaving the ethylene oxide absorber is supplied to an ethylene oxide stripper, wherein ethylene oxide is removed as a vapour stream. The ethylene oxide obtained from the ethylene oxide stripper can be purified for storage and sale or can be further reacted to provide monoethylene glycol.
In the process described in U.S. Pat. No. 6,080,897 and U.S. Pat. No. 6,187,972, ethylene oxide is catalytically reacted with carbon dioxide to produce ethylene carbonate. The ethylene carbonate is subsequently hydrolysed; the reaction of ethylene carbonate with water produces an ethylene glycol product stream. The product stream from the hydrolysis step is subjected to dehydration to remove water. The dehydrated stream is subjected to distillation wherein a glycol stream is removed from the top of the distillation column and a catalyst solution is removed from the bottom of the column. The catalyst solution is recycled to the carboxylation reactor.
EP 776 890 discloses a similar process wherein the product stream from the hydrolysis reactor is separated into a glycol stream and a catalyst solution. The catalyst solution is recycled to the ethylene oxide absorber. A portion of the catalyst solution is discharged as a catalyst bleed stream to avoid accumulation of heavy components such as diethylene glycol.
In addition to diethylene glycol, a catalyst bleed stream is likely to comprise catalyst degradation products, other impurities and monoethylene glycol. It is desirable to recover the monoethylene glycol from the catalyst bleed stream to increase the yield of the product. The present inventors have sought to provide a process that can be used to recover monoethylene glycol from a catalyst bleed stream. Desirably the process is integrated into the monoethylene glycol manufacturing process.